Automotive coolant



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Patented Aug. 4, 1953 AUTOMOTIVE COOLANT Ettore Da Fano, Raritan, N. J., assignor to John B. Pierce Foundation, New York, N. Y., a corporation of New York No Drawing. Application February 18, 1950, Se-

rial No. 145,083. 1949 7 Claims. 1

This invention relates to preparation of a heat transfer fluid which is especially adapted for use as a coolant in automobile radiators, and to the resulting fluid-mixture of organic isoalkyl aryl orthosilioates.

The, Johnston U. S. Patent No. 2,335,012 dis- In Great Britain May 26,

closes tetraaryl orthosilicates and their preparation. It also discloses mixtures of various tetraaryl orthosilicates with tetraalkyl orthosilicates.

A heat transfer fluid for automobile or the like cooling systems should be free flowing and stable up to a temperature of at least about 375 F., down to the lowest atmospheric temperature encountered in service. In addition, it should be resistant toward hydrolysis in the presence of water.

Tetraaryl orthosilicates are unstable toward hydrolysis in the presence of water. Moreover, the hydrolyzed products are insoluble, so that this unstability may quite readily lead to clogging of the cooling system of an automobile containing such a fluid, if a small amount of water were present when the fluid were added, or if the water were subsequently added by mistake or through condensation. Since it is extremely difficult or practically impossible to remove the hydrolysis product formed when the orthosilicates are so decomposed, the automobile radiator and engine block may be ruined thereby.

It has been found in accordance with the invention that a composition consisting essentially of isoalkyl aryl orthosilicates has the desired stability and fluidity up to about 375 F. and low temperature fluidity. These silicates can be proportioned to have any desired fluidity at temperatures as low as 100 F. In addition they are not objectionably unstable toward hydrolysis in the presence of water, and therefore such a mixture is an ideal heat transfer fluid for an automobile cooling system. Any aryl radical may be used. The isoalkyl radical has a small number of carbon atoms, generally less than about 6, and preferably is an isopropyl or isobutyl radical. There may be one or more different isoalkyl and/or aryl radicals in the mixture.

It has been observed that at elevated temperatures any mixture of organic orthosilicates tends to disproportionate due to interchange'of the organic radicals, and at equilibrium the various possible compounds will be present in certain relative proportions. To reduce the amount or concentration of the undesirable compounds, i. e.

those which decompose in water to form ob- I jectionable hydrolysates, the relative proportion of the organic groups which do not display this effect should be very high.

In order to understand the relation of the various organic groups, reference may be had to the preparation of the mixture of orthosilicates, which may be represented as follows:

where R is aryl or isoalkyl. If the organic reactant is a mixture, the R may be represented asa mixture of R. and R", where R is a lower isoalkyl radical and R is an aromatic radical. The following compounds are possible when only one isoalkyl and one aryl radical are present:

1. Tetraisoalkyl orthosilicate RO 0-R /Si RO \OR 2. Triisoalkylaryl orthosilicate R -0 0-11" /S1\ RO 04v 3. Diisoalkyldiaryl orthosilicate N R-O 0-11" 4. Isoalkyltriaryl orthosilicate I R-O OR R-O o 5. Tetraaryl orthosilicate gram radical weights) in the orthosilicates ofv the mixture should be such that the dispropor tionated equilibrium mixture will have the desired stability against hydrolysis in the presence of water and also the desired fluidity at low tem-:

peratures, for example, a mixture of: 50% triisopropylphenyl silicate and 50% diisopropyldiphenyl silicate disproportionates to the following mixture:

5.8% tetraisopropyl orthosilicate 37.1% triisopropylphenyl orthosilicate 36.9% diisopropyldiphenyl orthosilicate In order to avoid the necessity of such a compromise in cases where one of the above compositions will not meet the needs, a mixture of isopropyl radicals with isobutyl radicals is de- 17.5% isopropyltriphenyl orthosilicate 5 mlxture has 2 m 2.7% tetraphenyl orthosilicate proper y me udmg Verylow leezm" pom This may be due to the still greater number of This equilibrium mixture does not have the (1 compounds present upon disproportionation or sired stability against hydrolysis in the presence, equilibrium. Any proportion of isopropyl and of water, and this is thought to be due to the 10 isobutyl di l may b d, E on mic sugp s f too h a P portion of p e yl geststhat the isobutyl alcohol would not be subicals, Particularly in the last tWdm H' stituted for the isopropyl alcohol entirely and compounds. would'not be'used in a larger proportion than h fo g proportions of yl and isoalkyl necessarybecauseof its higher cost. A satisradicals in a mixture of the silicates fall withirdi factory composition is as follows! the requirements of the invention .andarefoun to have the desired fluidity or low viscosity at Radicals (gram radical weights) low temperatures and also the desired stability I H against hydrolysis in the presence of water: Example (isoililtyl) (isoplsopyl) 1, ,12% Ratio of radicals (based on their gram radical weights) 4 11 1 4 En mp1 GINO R R, I S l04 This is to be compared with Example No. 1 ex- (lsoalkyl) (511mm) cept that a part of the isopropyl is replaced by e isobutyl. It has the excellent hydrolysis resist- 5 f; ance of Example No. l, but has a cloud point 13 3 4 of 65 F., and a freezing point so low that it 12 4 4 has not been reached by cooling methods readily available. Similar benefits are obtainable by In the abovecase one or more isoalkyl mixtures of isopropyl and other isoalky1 radicals, aryl radicals maybe present. Any aryl radical such as 1 orisoamyL may be used, S s the p l radical, which The desired heat transfer fluid for use as a may contain one or more substituents, such as coolant in an automobile may be made (1) by m yl, e pr pyl, i p yl, an t like reacting sick with the desired mixture of an alkyl or other g p Mixtures of P11911371 isoalkyl alcohol ,or alcohols and a phenol, or (2) su stituted ph yl r other a radicals ay be by mixing the tetraisoalkyl orthosilicate with a pr nt, p vid n t e v r mixture s the diisoalkyldiaryl orthosilicate, or by mixing tetrad s r d y a ity p p s- Within isoalkyl orthosilicate with tetraaryl orthosilicate the above limits the aryl radical does not appear i corresponding proportions, and then carrying to be critical. out the disproportionation reaction.

The isoalkyl radical may be isopropyl, isobutyl, In the method (1) of making the silicates from sec-butyl, isoamyl, isohexyl; sec-amyl, a mixture thestarting alcohols orphenols and the silicon of isopropyl and isobutyl, a mixture of is p pyl tetrachloride, it is preferred that the reaction be and sec-butyl, and like-mixtures of other isoalkyl conducted out of contact with iron, since exradicals. Radicals having fewer than 6 carbon perience indicates that the presence of iron has atoms with a branch in the carbon chain close a deleterious effecton the yield, The isoproto the carbon affixed to. the oxysilicon group are panol and/or isobutanol and phenol are reacted preferred. with silicon tetrachloride in the desired propor- When the isoalkyl radical is the isopropyl tions, preferably using an excess of the alcohol radical, the composition varies in, properties and of the phenol. The mixture of alcohol and somewhat depending on the proportions within phenol may be added gradually to the silicon the above range. All of these proportions give tetrachloride, with agitation. The reaction is such high temperature stability as is needed in endothermic. After all the reactants are mixed, an automotive coolant. The higher the proporthe reaction mixture is heated to drive oil the tion of isopropyl radicals, the greater is the reresidual by-product hydrogen chloride. sistance to hydrolysis but the higher is the freez- Alternatively, the silicon tetrachloride may be ing point. For example, Examples Nos. 1 and added gradually to the mixture of alcohol and 2, which have the best resistance to hydrolysis, phenol, with agitation. In this procedure, during have freezing points (incipient crystallization on the first half of the addition, the reaction seems cooling to form a pumpa'ble mixture of crystals to be exothermic and no hydrogen chloride is and, liquid) of about 22 to 30 F, Examevolved. However, during the second half of the pie 4, on the other, hand, has a much lower addition, hydrogen chloride is evolved and the freezing point, but represents the maximum overall reaction is endothermic. amount of the aryl radical to be suitable against Near the end of the reaction metallic sodium hydrolysis. The proportions will be selected with 5 or a sodium compound of one or both of the two these twoproperties in mind, In climates where alcohols (sodium alcoholate) may be added, and temperatures never go below about 25 F., Exthis assists in bringing the reaction to completion amples Nos. 1 and 2 are preferable because of and in removing. the last traces of chlorinated their superior resistance to hydrolysis. Examcompounds. ple No. 3 is areasonable compromise in that it The reactants may be pure, or technical grade hasa free ing point of --70 F, and a cloud point materials may be used. The alcohol may contain (the temperature-at which on heating the mixup to 2 7:, water; and in this case, certain ture cloudiness disappears) of -22 F. and satpolymers will be formed, but their presence does isfactory resistance to hydrolysis fOr most pur not seem harmful since they do not materially poses, affect the stability of the mixture against hydrolysis in the presence of water, and they tend to lower the solidification point of the mixture.

The following general method (1) may be used for preparing Examples Nos. (1) to (5):

The equipment consists of a mechanically agitated reactor which can be heated or cooled at will; an adequate condenser or system of condensers suitable for both reflux and distillation; an acid absorbing trap; an alcohol trap to absorb and react with any entrained SiCh; a system of drying towers to prevent moisture from entering the reaction chamber; and a means of adding SlC14.

The reaction vessel is charged with isopropanol and/or isobutanol and phenol and the mixture is agitated to insure the solution of the phenol. The condenser is now connected, for reflux, to the acid absorber through the alcohol trap which contains excess of the total combined weights of the alcohols. The drying towers are placed so that no moisture can enter the system from the alcohol trap to the SiCl4 addition container.

The reactor is now cooled to between 0-5 C., at which point the SiCll is added at such a rate that the pot temperature does not exceed 25 C. The reaction, for the first half, is exothermic, mainly due to the heats of formation and solution of HCl, the main by-product; the second half, which is endothermic, due to the heat of dissolution of H01, begins when the temperature is such that HCl is no longer being dissolved in the reaction mixture. This point is usually reached when slightly more than half of the Sick has been added. A small amount of H20 insoluble gas (propylene-like odor) comes over in conjunction with the HCl evolution.

The addition of SiCli takes from 4 /2 to 6% hours, depending on the amounts and the emciency of the cooling system and the capacity of the HCl absorber. After the endothermic phase of the reaction begins the SiCh rate of addition can be speeded appreciably.

When the SiCll has all been added, the reactor cooling system is stopped. The liquid is brought slowly to room temperature and then heated to expel all HCl (ca. 125 C.). The reaction mixture is then allowed to reflux for at least ten (10) hours, but preferably longer.

The condenser is now arranged for distillation, and the unreacted materials are stripped off. The reactor is allowed to cool.

If desired, 10% excess alcohols may be added, and the whole brought to reflux. After refluxing for 12 hours, or more, the excess alcohols are stripped off. The volume of alcohols stripped off at this point may be less than the original volume.

After the reaction is complete, the reaction mixture is washed with water until the water phase is neutral to litmus. The liquid is then dried over Drierite (09.804) and filtered. The resultant silicate is a clear straw liquid of pleasant odor. The yield is between 90-95 per cent of theory.

The other method (2) is based on radical interchange. Amounts of pure isoalkyl silicates and aryl silicates (or amounts of mixed compounds) to give the desired proportion of isoalkyl and aryl radicals are mixed together and caused to transesterify or disproportionate. This reaction is slow in the absence of a catalyst. However, in the presence of a catalyst the reaction goes to completion in the order of a day at elevated temperatures under reflux. Catalysts for coolant does not need to be distilled, except for topping off the excess alcohols used. The material is suiilciently purified by washing it thoroughly with water, using one of the washing devices already used for similar purposes. Three washings are recommended. The first water hydrolyzes and removes any chlorosilicate present, either because it was formed by the synthesis or because it was added as a catalyst. Gelatinous silicic acid deposits on the interface between water and silicate. It is easily removed by separation in a device of the general shape of a separatory funnel. At the same time some dark colored impurities contained in the crude material are removed and the resulting liquid is much lighter in color than the crude material. The wash water on which the silicate floats is acid because of HCl. After the second washing, the water is practically neutral but may occasionally contain small amounts of acid. A third washing assures neutrality. Because of the resistance of the composition to hydrolysis, there is no deleterious effect due to washing. After the washing the material should be filtered.

All parts and percentages in the specification and claims are by weight.

I claim:

1. A composition suitable for use as an automotive coolant, consisting essentially of a mixture of isoalkyl orthosilicates, mononuclear hydrocarbon aryl orthosilicates and mixed mononuclear hydrocarbon aryl isoalkyl orthosilicates, in proportions such that the mixture has 12 to 15 isoalkyl radicals and 4 to l mononuclear hydrocarbon aryl radicals for each 4 silicate radicals, said isoalkyl radical having less than 6 carbon atoms.

2. A composition in accordance with claim 1 in which the isoalkyl radical is the isopropyl radical.

3. A composition in accordance with claim 1 in which the isoalkyl radical is the isopropyl radical and the mononuclear aryl radical is the phenyl radical.

4. A composition in accordance with claim 1 in which the aryl radical is the phenyl radical.

5. A composition in accordance with claim 1 in which the isoalkyl radical is a mixture of isopropyl and isobutyl radicals.

6. A composition in accordance with claim 1 in which the isoalkyl radical is a mixture of isopropyl and isobutyl radicals and the mononuclear aryl radical is the phenyl radical.

7. A composition in accordance with claim 5 in which the isopropyl radicals and the isobutyl radicals are in the proportion of 11 to 4 gramradical weights.

ETTORE DA FANO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,053,474 Graves Sept. 8, 1936 2,335,012 Johnston Nov. 23, 1943 2,566,365 Pedlow, Jr. Sept. 4, 1951 

1. A COMPOSITION SUITABLE FOR USE AS AN AUTOMOTIVE COOLANT, CONSISTING ESSENTIALLY OF A MIXTURE OF ISOALKYL ORTHOSILICATES, MONONUCLEAR HYDROCARBON ARYL ORTHOSILICATES AND MIXED MONONUCLEAR HYDROCARBON ARYL ISOALKYL ORTTHOSILICATES, IN PROPORTIONS SUCH THAT THE MIXTURE HAS 12 TO 15 ISOALKYL RADICALS AND 4 TO 1 MONONUCLEAR HYDROCARBON ARYL RADICALS FOR EACH 4 SILICATE RADICALS, SAID ISOALKYL RADICAL HAVING LESS THAN 6 CARBON ATOMS. 